The present invention generally relates to RF tuners. More specifically, the present invention relates to a tracking amplifier and a band-pass impedance generator for tuning input RF signals.
Broadband cable and terrestrial systems offer consumers a wide range of channels, which are spread over a broad range of RF frequencies. RF frequencies are usually in the 50-860 MHz range, with each channel having a bandwidth of 6, 7 or 8 MHz. Various products, such as television sets, set-top boxes, computer systems, and the like, deploy RF tuners (also referred to as broadband tuners) to tune to a desired channel by filtering undesired channels without altering the information carried by the desired channel.
Various filtering techniques are used by RF tuners for channel selection, e.g., variable-frequency filters and fixed-frequency filters. Variable-frequency filters are usually used in Single Conversion Tuners (SCT) and fixed-frequency filters in Double Conversion Tuners. A Double Conversion Tuner uses a fixed-frequency band-pass filter such as a SAW filter, preceded and followed by mixing stages. The first mixing stage up-converts the entire block of input RF signal frequencies to an Intermediate Frequency IF1. The entire up-converted block of input RF signal frequencies is then passed through the fixed-frequency band-pass filter to reject undesired frequencies. The second mixing down-converts the desired channel frequency to a standard Intermediate Frequency (IF), which is used for further processing. However, the use of external band-pass filters downgrades the process of system integration and increases the cost. Further, the first up-conversion process for the entire block of the input RF signal frequencies increases power consumption, which, in turn, causes high power dissipation and thus heat.
A Single Conversion Tuner performs a single mixing operation. Prior to mixing, the input RF signal frequencies are passed through a variable input band-pass filter. The variable-frequency band-pass filter (also referred to as tracking filter) rejects all other frequencies except the desired signal (also referred to as an in-band signal) frequency. The in-band signal frequency is then down-converted to a standard Intermediate Frequency (IF) by using a mixer. The IF is used to process the signal further. However, the variable-frequency filters used in SCTs need to be extremely accurate, perform very efficiently, and have a high quality factor (Q). They require extremely accurate and precise variable filter elements such as hand-tunable, high-Q wire-wound inductors, and the like. However, these elements are difficult to integrate on a single chip.
In light of the foregoing, there is a need for an RF tuner that does not require external components such as a SAW filter and has improved power dissipation. Further, there is a need to do away with discrete components such as inductors, capacitors, diodes, and the like, which face significant difficulty during the process of integration.